The present invention relates to a press, such as a folding press or a deep-draw press, which comprises a press frame with a lower yoke and an upper yoke which are mutually reciprocally movable with reciprocating means, wherein the lower yoke and the upper yoke are each provided with co-acting tools and wherein between a yoke and its tool are arranged curve-forming means which comprise at least one pair of curve-forming wedges.
Such a press is known and is provided with curve-forming devices for the purpose of compensating during pressing or bending for deformations occurring in the diverse components of the press as well as in the materials for shaping.
EP-A-67.766 describes a press wherein the curve-forming means are formed by one pair of curve-forming wedges extending over the whole length of the press. The top wedge is provided along its length with a number of bolts which via a toothed wheel are all connected mutually and to an adjusting motor by means of a chain. A variation in the sideways movement of the top wedge 7 along its length is possible due to a difference in mutual pitch of the bolts or a differing number of teeth of a toothed wheel for a bolt.
EP-A-330.258 describes a press wherein the curve-forming wedges of a pair are mutually slidable in lengthwise direction of the press. In order to reduce the total height of a curve-forming wedge pair each curve-forming wedge can be embodied as two mutually connected wedge portions, the wedge surfaces of which connect to one another discontinuously.
Variations can be of diverse origin:
a) during pressing or bending the press sags as a consequence of the applied load. This sag line can be calculated but varies depending on the case of loading. When the load is short and concentrated the sag line has a shape other than with a load which runs the support points of the reciprocating means, for example the hydraulic cylinders. Extreme variations occur if the load extends laterally beyond the support points or if the press is loaded eccentrically;
b) the lower yoke and the upper yoke and the tools have linearity deviations, the consequences of which are recognizable in the pressed or bent products;
c) the tools used generally have dimensional variations which can only be reduced at increasingly excessive cost;
d) as a result of wear, location-dependent dimensional variations occur in the tools used; and
e) the material used that is to be worked is not completely homogeneous (grain size distribution), has no constant material thickness and has unevenly distributed stresses, as a result among other things of rolling, so that location-dependent varying deformation properties occur.
A number of these variations are predictable, a number of other variations vary or manifest themselves during prolonged use of the press or in the case of use of different materials for working. There therefore exists a need for curve-forming means that are adjustable optimally and as accurately as possible. This adjustment has preferably to be possible independently from place to place along the length of the yoke.
It is moreover desirable that the curve-forming means have the simplest possible form and construction.